1. Field of the Invention
The present invention relates to a slider of a thin-film magnetic head which comprises a medium facing surface that faces toward a recording medium and a thin-film magnetic head element located near the medium facing surface, and to a method of manufacturing such a slider.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element (that may be hereinafter called an MR element) for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using a GMR element is called a GMR head. An AMR head is used as a reproducing head where areal recording density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head where areal recording density is more than 3 gigabits per square inch. It is GMR heads that have been most widely used recently.
Performance of the reproducing head is improved by replacing the AMR film with a GMR film and the like having an excellent magnetoresistive sensitivity. Alternatively, a pattern width such as the reproducing track width and the MR height, in particular, may be optimized. The MR height is the length (height) between an end of the MR element located in the air bearing surface and the other end. The air bearing surface is a surface of the thin-film magnetic head facing toward a magnetic recording medium.
Performance improvements in a recording head are also required as the performance of a reproducing head is improved. It is required to increase the recording track density in order to increase the areal recording density among the performance characteristics of the recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein the width of top and bottom poles sandwiching the recording gap layer on a side of the air bearing surface is reduced down to microns or a submicron order. Semiconductor process techniques are utilized to implement such a structure. A pattern width, such as the throat height in particular, is also a factor that determines the recording head performance. The throat height is the length (height) of pole portions, that is, portions of magnetic pole layers facing each other with a recording gap layer in between, between the air-bearing-surface-side end and the other end. To achieve improvement in the recording head performance, it is desirable to reduce the throat height. The throat height is controlled by an amount of lapping when the air bearing surface is processed.
As thus described, it is important to fabricate well-balanced recording and reproducing heads to improve the performance of the thin-film magnetic head.
In order to implement a thin-film magnetic head that achieves high recording density, the requirements for the reproducing head include a reduction in reproducing track width, an increase in reproducing output, and a reduction in noise. The requirements for the recording head include a reduction in recording track width, an improvement in overwrite property that is a parameter indicating one of characteristics when data is written over existing data, and an improvement in nonlinear transition shift.
In general, a flying-type thin-film magnetic head used in a hard disk drive and the like is made up of a slider having a thin-film magnetic head element formed at the trailing edge thereof. The slider slightly flies over a recording medium by means of airflow generated by the rotation of the medium.
Reference is now made to FIGS. 32A to 35A, FIGS. 32B to 35B, and FIG. 36 to describe an example of a method of manufacturing a related-art thin-film magnetic head element. FIGS. 32A to 35A are cross sections each orthogonal to the air bearing surface. FIGS. 32B to 35B are cross sections of the pole portion each parallel to the air bearing surface.
According to the manufacturing method, as shown in FIGS. 32A and 32B, an insulating layer 102 made of alumina (Al2O3), for example, is deposited to a thickness of about 5 to 10 μm on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. Next, on the insulating layer 102, a bottom shield layer 103 made of a magnetic material is formed for a reproducing head.
On the bottom shield layer 103, a bottom shield gap film 104 made of an insulating material such as alumina is formed to a thickness of 100 to 200 nm, for example, through a technique such as sputtering. On the bottom shield gap film 104, an MR element 105 for reproduction is formed to a thickness of tens of nanometers. Next, a pair of electrode layers 106 are formed to be electrically connected to the MR element 105 on the bottom shield gap film 104.
Next, a top shield gap film 107 made of an insulating material such as alumina is formed through sputtering, for example, on the bottom shield gap film 104, the MR element 105 and the electrode layers 106. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, on the top shield gap film 107, a top-shield-layer-cum-bottom-pole layer (called a bottom pole layer in the following description) 108 having a thickness of about 3 μm is formed. The bottom pole layer 108 is made of a magnetic material and used for both the reproducing head and the recording head.
Next, as shown in FIGS. 33A and 33B, a recording gap layer 109 made of an insulating film such as an alumina film and having a thickness of 0.2 μm is formed on the bottom pole layer 108. Next, the recording gap layer 109 is partially etched to form a contact hole 109a for making a magnetic path. Next, a top pole tip 110 for the recording head is formed on the recording gap layer 109 in the pole portion. The top pole tip 110 is made of a magnetic material and has a thickness of 0.5 to 1.0 μm. At the same time, a magnetic layer 119 made of a magnetic material is formed for making the magnetic path in the contact hole 109a for making the magnetic path.
Next, as shown in FIGS. 34A and 34B, the recording gap layer 109 and the bottom pole layer 108 are etched through ion milling, using the top pole tip 110 as a mask. As shown in FIG. 34B, the structure is called a trim structure wherein the sidewalls of the top pole portion (the top pole tip 110), the recording gap layer 109, and a part of the bottom pole layer 108 are formed vertically in a self-aligned manner.
Next, an insulating layer 111 of alumina, for example, having a thickness of about 3 μm, is formed over the entire surface. The insulating layer 111 is polished to the surfaces of the top pole tip 110 and the magnetic layer 119 and flattened.
On the flattened insulating layer 111 a first layer 112 of a thin-film coil, made of copper (Cu), for example, is formed for the induction-type recording head. Next, a photoresist layer 113 is formed into a specific shape on the insulating layer 111 and the first layer 112 of the coil. Heat treatment is performed at a specific temperature to flatten the surface of the photoresist layer 113. Next, a second layer 114 of the thin-film coil is formed on the photoresist layer 113. Next, a photoresist layer 115 is formed into a specific shape on the photoresist layer 113 and the second layer 114 of the coil. Heat treatment is performed at a specific temperature to flatten the surface of the photoresist layer 115.
Next, as shown in FIGS. 35A and 35B, a top pole layer 116 for the recording head is formed on the top pole tip 110, the photoresist layers 113 and 115 and the magnetic layer 119. The top pole layer 116 is made of a magnetic material such as Permalloy (NiFe). Next, an overcoat layer 117 of alumina, for example, is formed to cover the top pole layer 116. Finally, machine processing of the slider including the forgoing layers is performed to form the air bearing surface 118 of the recording head and the reproducing head. The thin-film magnetic head element is thus completed.
FIG. 36 is a top view of the thin-film magnetic head element shown in FIGS. 35A and 35B. The overcoat layer 117 and the other insulating layers and films are omitted in FIG. 36.
Reference is now made to FIGS. 37 to 42 to describe the configuration and functions of a related-art slider. FIG. 37 is a bottom view showing an example of the configuration of the air bearing surface of the related-art slider. FIG. 38 is a perspective view of the related-art slider. In the example shown in FIGS. 37 and 38, the air bearing surface of the slider 120 is shaped such that the slider 120 slightly flies over the surface of a recording medium such as a magnetic disk by means of airflow generated by the rotation of the recording medium. In this example, a thin-film magnetic head element 122 is disposed at a position near the air outflow end of the slider 120 (the end on the upper side of FIG. 37) and near the air bearing surface thereof. The configuration of the thin-film magnetic head element 122 is as shown in FIGS. 35A and 35B, for example. Portion A of FIG. 37 corresponds to FIG. 35B.
In the example shown in FIGS. 37 and 38, the air bearing surface of the slider 120 has first surfaces 121a that are closest to the recording medium, a second surface 121b having a first difference in level from the first surfaces 121a, and a third surface 121c having a second difference in level, greater than the first difference in level, from the first surfaces 121a. The first surfaces 121a are disposed near both sides along the width of the slider 120 (the lateral direction in FIG. 37) and around the thin-film magnetic head element 122. The second surface 121b is disposed near the air inflow end (the end on the lower side of FIG. 37). The remaining part of the air bearing surface, i.e., the part other than the first and second surfaces 121a and 121b, constitutes the third surface 121c. The first difference in level between the first and second surfaces 121a and 121b is about 1 μm. The second difference in level between the first and third surfaces 121a and 121c is about 2 to 3 μm.
While the recording medium is rotating, a pressure is created between the recording medium and the first surfaces 121a of the air bearing surface of the slider 120 shown in FIGS. 37 and 38, the pressure moving the slider 120 away from the recording medium. In the air bearing surface of the slider 120 shown in FIGS. 37 and 38, the second surface 121b is disposed near the air inflow end, and the third surface 121c is disposed closer to the air outflow end than the second surface 121b is. Here, while the recording medium is rotating, the air passing through between the second surface 121b and the recording medium increases in volume when it reaches the space between the third surface 121c and the recording medium. Accordingly, a negative pressure to draw the slider 120 toward the recording medium is generated between the third surface 121c and the recording medium. As a result, while the recording medium is rotating, the slider 120 flies over the recording medium, being inclined such that the air outflow end is closer to the recording medium than the air inflow end is. The inclination of the air bearing surface of the slider 120 with respect to the surface of the recording medium is designed to fall within 1°, for example. The amount of flying of the slider 120 can be reduced by appropriately designing the shape of the air bearing surface.
The slider 120 is fabricated as follows. First, a wafer that includes a plurality of rows of portions to be sliders (hereinafter called slider portions), each of the slider portions including the thin-film magnetic head element 122, is cut in one direction to form blocks called bars each of which includes a row of slider portions. The surface of this bar to be the air bearing surface is then lapped into a lapped surface. Then, first photoresist masks are formed by photolithography on a portion of this lapped surface, the portion being to be the first surfaces 121a. Using the first photoresist masks, the lapped surface is selectively etched to form a stepped surface that has the first difference in level from the lapped surface. The first photoresist masks are then removed. Then, a second photoresist mask is formed by photolithography on the portion of the lapped surface that is to be the first surfaces 121a and on a portion of the stepped surface, the portion being to be the second surface 121b. Using this second photoresist mask, the stepped surface is selectively etched to form the third surface 121c having the second difference in level from the lapped surface. In this way, the first surfaces 121a, the second surface 121b, and the third surface 121c are formed. Then, the bar is cut into the individual sliders 120.
FIG. 39 is a cross section illustrating the slider 120 and a recording medium 140 in a state in which the recording medium 140 is at rest. In FIG. 39, the slider 120 is shown as sectioned along line 39—39 of FIG. 37. FIG. 40 shows the slider 120 as viewed from the upper side of FIG. 37.
As shown in FIG. 39, the greater part of the slider 120 is made up of the substrate 101 made of aluminum oxide and titanium carbide, for example. The rest of the slider 120 is made up of an insulating portion 127 made of alumina, for example, and the thin-film magnetic head element 122 and so on formed in the insulating portion 127. The greater part of the insulating portion 127 is the overcoat layer 117.
In the slider 120 shown in FIGS. 39 and 40, a protection layer 128, made of diamond-like carbon (DLC) or the like, is formed on the air bearing surface so as to protect the bottom shield layer 103, the bottom pole layer 108, the top pole tip 110, the top pole layer 116 and others from corrosion.
FIG. 41 is a cross section illustrating the slider 120 and the recording medium 140 in a state in which the recording medium 140 has just started rotation from a resting state. FIG. 42 shows a state in which the recording medium 140 is rotating and the slider 120 is flying over the surface of the recording medium 140 to perform reading and writing with the thin-film magnetic head element 122. While the slider 120 is flying, the minimum distance H11 between the slider 120 and the recording medium 140 is about 8 to 10 nm, and the distance H12 between the air outflow end of the slider 120 and the recording medium 140 is about 100 to 500 nm.
Measures for improving the performance of a hard disk drive, such as areal recording density in particular, include increasing a linear recording density and increasing a track density. To design a high-performance hard disk drive, specific measures to be taken for implementing the recording head, the reproducing head or the thin-film magnetic head as a whole differ depending on whether linear recording density or track density is emphasized. That is, if priority is given to track density, a reduction in track width is required for both the recording head and the reproducing head, for example.
If priority is given to linear recording density, it is required for the reproducing head, for example, to improve the reproducing output and to reduce a shield gap length, that is, the distance between the bottom shield layer and the top shield layer. Furthermore, it is required to reduce the distance between the recording medium and the thin-film magnetic head element (hereinafter called a magnetic space).
A reduction in magnetic space is achieved by reducing the amount of flying of the slider. A reduction in magnetic space contributes not only to an improvement in the reproducing output of the reproducing head but also to an improvement in the overwrite property of the recording head.
The amount of flying of the slider can be reduced, for example, by forming the first, second, and third surfaces having differences in level from one another in the air bearing surface of the slider as shown in FIGS. 37 and 38. As described before, however, the formation of the air bearing surface having such a configuration necessitates two steps of forming a photoresist mask and two steps of etching. Accordingly, forming the first through third surfaces of different levels from one another in the air bearing surface of the slider has a problem in that the number of steps for manufacturing the slider is large and the manufacturing costs of the slider is therefore high.
On the other hand, as the magnetic space is reduced, the slider is likely to collide with the recording medium, which can result in damage to the recording medium and the thin-film magnetic head element. To avoid this, it is required to enhance the smoothness of the surface of the medium. However, the slider easily sticks to the medium if the smoothness of the surface of the medium is enhanced. This results in a problem that the slider is harder to take off from the recording medium when the recording medium starts rotation from a resting state where the slider is in contact with the recording medium.
Conventionally, a crown or a camber is formed on the air bearing surface of the slider in order to prevent the slider from sticking to the recording medium. A crown refers to a convex surface which gently curves along the length of the slider 120 as shown in FIG. 39. A camber refers to a convex surface which gently curves along the width of the slider 120 as shown in FIG. 40. The crown has a difference of elevation C1 on the order of 10 to 50 nm. The camber has a difference of elevation C2 on the order of 5 to 20 nm.
Crowns are conventionally formed, for example, by changing the orientation of the bar with respect to the surface plate when lapping the air bearing surface of the bar.
Cambers are conventionally formed by the following method, for example. That is, after lapping the air bearing surface of the bar to adjust MR height, slits are made in the bar, using a diamond grinder or the like, at positions at which the slider portions are to be separated. Then, the air bearing surface of the bar is re-lapped lightly on a concave surface plate.
In the above-described method for forming cambers, after the MR height is precisely adjusted by lapping the air bearing surface of the bar, the air bearing surface of the bar is lapped again by about 10 to 20 nm in order to form the camber. This results in a problem that the MR height can deviate from its desired value. Further, according to this method, when the air bearing surface of the bar is lapped on the concave surface plate, the bar can be scratched by stain and dust on the surface plate, which results in a problem of a lower yield of the thin-film magnetic heads. Further, according to this method, when the air bearing surface of the bar is lapped on the concave surface plate, chippings of the electrode layer connected to the MR element may be jammed and spread between the air bearing surface and the surface plate, producing a defect called a smear. The smear sometimes causes an electric short circuit between the MR element and the shield layers. The short circuit can lower the sensitivity of the reproducing head and produce noise in the reproducing output, thereby deteriorating the performance of the reproducing head.
Further, if crowns/cambers are to be formed on the air bearing surfaces of the sliders, manufacturing costs of the sliders are raised because of the steps of forming the crowns/cambers.